SUMMARYThe degree of matching ofHLAgenes between the selected donor and recipient is an important aspect of the selection of unrelated donors for allogeneic bone marrow transplantation (UBMT). The most sensitive methods currently used are serological typing ofHLAclass I genes, mixed lymphocyte culture (MLC), IEF and molecular genotyping ofHLAclass II genes by direct sequencing of PCR products. Serological typing of class I antigenes(A, BandC)fails to detect minor differences demonstrated by direct sequencing of DNA polymorphic regions. Molecular genotyping ofHLAclass I genes by DNA analysis is costly and work‐intensive. To improve compatibility between donor and recipient, we have set up a new rapid and non‐radioisotopic application of the ‘fingerprinting PCR’ technique for the analysis of the polymorphic second exon of theHLAclass IA, Band C genes. This technique is based on the formation of specific patterns (PCR fingerprints) of homoduplexes and heterodu‐plexes between heterologous amplified DNA sequences. After an electrophoretic run on non‐denaturing polyacrylamide gel, differentHLAclass I types give allele‐specific banding patterns.HLAclass I matching is performed, after the gel has been soaked in ethidium bromide or silver‐stained, by visual comparison of patients’ fingerprints with those of donors. Identity can be confirmed by mixing donor and recipient DNAs in an amplification cross‐match. To assess the technique, 10 normal samples, 22 related allogeneic bone marrow transplanted pairs and 10 unrelatedHLA‐AandHLA‐Bserologically matched patient‐donor pairs were analysed forHLAclass I polymorphic regions. In all the related pairs and in 1/10 unrelated pairs, matched donor‐recipient patterns were identified. This new application of PCR fingerprinting may confirm theHLAclass I serological selection